1. Field of Invention
Embodiments described relate to magnetic drives for food processing equipment, particularly for food processing equipment including a food contact chamber separable from a motor drive unit, such as blenders, mixers and the like.
2. Discussion of Related Art
Conventional home blenders and mixers typically incorporate a mechanically-driven impeller rotatably mounted within a removable blender cup. The base of the cup incorporates a generally circular connection plate with a pattern of projections and/or depressions formed on its lower face that is removably mateable, using a vertical, drop-in movement, with a corresponding pattern formed on a like plate attached to the shaft of a motor housed in a base of the machine. This mechanical coupling between the blender cup and the blender motor often requires a rotary seal at the base of the cup between the impeller and connecting plate. This seal is subject to considerable wear and tear over time, as is the mechanical coupling. Because seal failure can result in liquid leaking out of the cup, the seal and bearings in the base of the cup are typically built to ensure sealing at the expense of friction. The friction produces wear, heat, and loss of power. Moreover, the conventional blender produces much unwanted noise, and the mechanical interlocking coupling between the plates can make it awkward or difficult to remove the cup from, and return the cup to, the base.
Many drink mixers have the drive motor mounted in the base directly under the cup. If overall height is a concern, however, the motor may be positioned off to the side and coupled to the driving shaft by a belt or gear arrangement.
A commercially viable blender/shaver for the production of frozen drinks should preferably satisfy a variety of special and important design criteria. It should be compact, both in its footprint and overall height, so as to utilize limited space at a bar efficiently. It ideally has a comparatively low weight. The straight-forward approach of placing a conventional electric motor directly under the blender cup increases the overall height of the machine, and therefore considered undesirable in connection with mechanical linkages.
There should also be speed control, typically provided through gearing and electronics, to accommodate different power and speed requirements in different phases of operation. Rapid controlled braking is also desirable to limit the overall time required to blend, to avoid splashing of the blended material after blending is complete, and for safety. Control of vibration, prevention of overheating, or minimization of wear, ease of maintenance, and durability are also important.
It has also been known that an impeller within a blender cup may be driven magnetically or electromagnetically rather than mechanically. One type of magnetic drive couples a rotating permanent magnet outside a blender cup or the like, to another permanent magnet rotatably mounted in the blender cup. U.S. Pat. No. 2,459,224 to Hendricks; U.S. Pat. No. 2,655,011 to Ihle et al.; and U.S. Pat. No. 5,478,149 to Quigg are exemplary of this approach. Hendricks discloses a magnetically operated stirrer for mixing liquids, in which the stirrer has a magnet mounted at its lower end and within the container for the liquid. Quigg discloses a motor that drives a set of magnets, via gear box and shaft, to couple to another set of magnets mounted on an agitator.
U.S. Pat. No. 3,140,079 to Baermann uses a large rotating plate to carry a series of circumferentially spaced magnets that pass under one portion of a much smaller, rotatable conductive disc.
U.S. Pat. No. 1,242,493 to Stringham and U.S. Pat. No. 1,420,773 to Stainbrook disclose electrical drink mixers in which a stator of an AC motor surrounds and interacts with a rotor in a blender cup, or in its base. In Stringham, a squirrel cage rotor lies in the plane of the stator windings. In Stainbrook, an alternating current (AC) rotor is mounted in the base of the blender cup and stator coils are located below the cup. Such split AC motor arrangements are limited by the torque, speed control, eddy current loss, and emf interference problems of a.c motors, as accentuated by the physical separation of the stator windings and the rotor. They often do not provide good speed control. They do not utilize a direct current (DC) magnetic field coupling. Further, the inclusion of the rotor of the motor within the container or cup often adds unwanted weight to the cup assembly and makes the cup difficult to handle due to gyroscopic effects if it is picked up while the rotor is still spinning.
If the permanent magnet rotor of a brushless DC motor were to be located in the base of a blender cup, the cup would not only become heavy and exhibit a severe gyroscopic effect, but it would also “stick” to steel or iron sinks and countertops, and would attract loose steel or iron objects such as some flatware, barware, or coins.
One or more of the present inventors have described magnetic drive food processing equipment in U.S. Pat. Nos. 6,095,677, 6,336,603, 6,210,033, and 6,793,167.